Assembled cathode and plasma igniter with such cathode

ABSTRACT

This invention relates to a plasma igniter for directly igniting the pulverized coal burner. Said plasma igniter consists of a plasma generator which includes a composite anode, an combined type cathode, an electromagnetic coil and a transmitting coil; a pulverized coal burner which comprises multi-stage chambers for conveying igniting coal, an equipment for adjusting concentration of coal powder and a four-stage burner canister; and a generator brace. Said combined type cathode consists of a cathode plate, a fixation nut, a conductive pipe, an inflowing pipe, an inflowing guiding pipe, a cathode lid and a sealing spacer. The lining for generating electric arc is assembled with the front of cathode. An alloy plate is used as the cathode plate. The nozzle that used for cooling the cathode is first convergent and then expansive, and is placed in the middle of the conductive pipe. The plasma igniter has the advantage of stable burning. It can be used as not only a main burner for the boiler but also an igniting burner. Since oil is not used, lots of petroleum source is saved.

Technical Field

[0001] The present invention relates to a cathode of a plasma ignitiondevice for directly igniting a pulverized coal burner, and a plasmaignition device using such a cathode and for directly starting apulverized coal boiler. The plasma ignition device is used in thestarting ignition stage and the low-load stable combustion stage of thepulverized coal boiler, and may serve as the primary burner of thepulverized coal boiler as well.

Background Art

[0002] The starting ignition and low-load stable combustion of theconventional industrial pulverized coal boiler rely on burning oil. Inthe year of 1999, the pulverized coal boilers of the state power systemof China consumed about 2.87 million tons of oil, amounting to about 10billion RMB yuan in value. Since the 1980's, the technologists ofdifferent countries focused on developing technologies adopting plasmatechnology in directly igniting the pulverized coal. An Australian hasdeveloped a plasma ignition device, in which the electrodes areprotected with nitrogen gas and fat coal is burned. The former SovietUnion has made a large amount of fundamental research and madeexperiments in power plants in Baoji and Shaoguan in China respectivelyin 1996 and 1998, but the experiments were not successful. The TsinghuaUniversity and Harerbin Boiler Factory in China. have also made a largeamount of research.

[0003] Various plasma ignition devices for directly igniting pulverizedcoal developed in different countries failed to achieve progress insome. important technical problems such as ensuring the continuousoperation of the generator and preventing the burner from coking, thushave not been adopted widely.

[0004] A patent of utility model of the applicant, no.99248829.x, hasdisclosed a plasma ignition device used in an axial flow type burneradopting bi-stage powder delivery. However, the burner has someshortcomings. To some extent, coking and ablation will occur. Inaddition, the coal type that can be burned in the burner is unique andthe burner's operation is unstable. For example, the cathode of theburner is a graphite rod, which tends to drop scraps during operationand lead to short circuit and make the voltage unstable.

[0005] For overcoming said shortcomings, the applicant filed and wasgranted a patent for utility mode no.00245774.l, entitled as “metalelectrodes used in plasma ignition device”. The electrode disclosed inthe patent still has some shortcomings: the anode tends to be damagedduring arc starting, the voltage waves greatly, the cathode is short inlife and expensive. Therefore, the wide application of the plasmaignition device is influenced adversely.

SUMMARY OF THE INVENTION

[0006] Therefore, an object of the invention is to provide a combinedtype cathode used in plasma ignition device.

[0007] Said object is realized by the following cathode. A combined typecathode used in a plasma ignition device, comprises cathode head, tightnuts, electrically conductive tube, water inlet tube, water inlet pipe,water outlet tube, cathode end cap and sealing cushion, said cathodehead is welded to the tight nuts of copper, said electrically conductivetube is jointed to the nuts by screwed connection, a water inlet tube isinserted into the other end of the electrically conductive tube, and isjointed thereto by welding or screwed connection, a water outlet tube ismounted by welding in the direction perpendicular to the electricallyconductive tube, thereby a cooling system of the cathode is formed,characterized in that on the front end of the cathode is mounted adedicated arc-starting bush, the cathode plate is made of alloy plate,and a cooling nozzle is adopted. Said cooling nozzle is constructed sothat it is first convergent and then divergent.

[0008] Under normal operation condition, the inventive combined typecathode has the following properties:. self-contracting electric arc,stable voltage, long cycle-life, few burning loss of the anode duringarc starting, considerably reduced cost. Therefore, the reliability ofthe plasma ignition device is improved.

[0009] Another object of the invention is to provide a plasma ignitiondevice for directly igniting a pulverized coal burner, in which theplasma generator can operate continuously and stably, while ensuringthat the pulverized coal burner is not easily subject to coking orburning loss, thus operates reliably.

[0010] Above object is realized by a plasma ignition device for directlystarting a pulverized coal boiler, comprises plasma generator,pulverized coal burner and dc power supply, wherein said plasmagenerator comprises combined type cathode, composite anode,electromagnetic coil, arc-starting coil mounted surrounding the housingof the composite anode, and linear motor, and said pulverized coalburner comprises burner nozzle, four stages of burning chambers,powder-air tubes, primary air-powder tube, guide plates,high-temperature plasma transporting pipe andpowder-concentration-adjusting guide plate.

[0011] According to a preferred embodiment of the invention, saidcomposite anode is in form of double nozzle tubes. Said anode body ismade of material having high thermal conductivity and high electricalconductivity and the oxide of which is also electrically conductive,preferably Ag-based alloy, and the anode nozzle may be made of Ag-basedalloy or red copper. Said combined type cathode comprises cathode head,arc-starting bush, tight nuts, cathode plate, cooling nozzle,electrically conductive tube, water inlet tube, water inlet pipe, wateroutlet tube, electrically conductive tube and cathode end cap. Saidcathode plate is in shape of a cylinder plus a cone, and is attached tothe cathode head through welding, and is made of Ag-based material, thecooling nozzle is constructed so that it is convergent first and thendivergent.

[0012] Since the combined type cathode adopts high-velocity nozzle withforced cooling, the heat transmission of the cathode is accelerated andthe life of the cathode is lengthened. The life of the cathode isfurther improved through adopting good electrically conductive and goodthermally conductive material, preferably Ag-based material as cathodeplate.

[0013] Through adopting the composite anode, the flow field of theplasma in the inner cavity of the anode is changed. In particular, atthe nozzle, the axial component of the flow is dominant, and thus theanode is prevented from being contaminated by the pulverized coal. Inaddition, since the receiving area of the anode is increased on thebasis of the conventional nozzle, the electrons are received within theanode nozzle tube, and thus will not be disturbed by any externaldynamic field, and thus the output power of the equipment is verystable. The arc-transporting coil coated outside of the composite anodeincreases the length of the plasma flame, and thus improve the abilityof igniting the pulverized coal.

[0014] Furthermore, adopting multi-stage axial powder delivery and gasfilm cooling techniques, and performing ignition through stage-by-stageamplification, which increase greatly the output power of the burnerwith lower power consumption, the burner has functions of ignition andstable combustion, as well as serving as primary burner. Specifically,auxiliary air is adopted to perform air film cooling of the first,second, third and fourth burning chambers, so that the wall temperatureof the burning chambers is decreased below the ash fusion temperatureand coking is prevented. In,the third stage burning chamber, the oxygenis supplemented by the low concentration powder flow; in the fourthburning chamber, the oxygen is supplemented by the auxiliary air, sothat the burning is enhanced and the rigidity of the flame is improved.

[0015] Therefore, the inventive plasma ignition device has advantages ofgreat power, no coking, high burning efficiency, strong rigidity offlame, and various coals can be burned therein. Since the inventiveequipment solves the key techniques relating to the continuous andstable operation of high power plasma ignition device, the inventiveplasma ignition device may be widely applied in industrial pulverizedcoal boiler. The conventional method of starting and igniting industrialboiler and making it stably operating with oil will be replaced, and alarge amount of petroleum will be saved.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The preferred embodiments of the present invention will bediscussed in details with reference to the accompanying drawings, inwhich,

[0017]FIG. 1 is a diagram illustrating the structure of a plasmaignition device for directly igniting a pulverized coal boiler accordingto the present invention;

[0018]Fig. 2 is a diagram illustrating the structure of a pulverizedcoal burner of the plasma ignition device for directly igniting apulverized coal boiler according to the present invention;

[0019]Fig. 3 is a diagram illustrating the structure of a combined typecathode of the plasma ignition device for directly igniting a pulverizedcoal boiler according to the present invention;

[0020]FIG. 4 is a diagram illustrating the structure of a compositeanode of the plasma ignition device for directly igniting a pulverizedcoal boiler according to the present invention;

[0021]FIG. 5 is a diagram illustrating the operating principle of theplasma ignition device for directly igniting a pulverized coal boileraccording to the present invention;

[0022]FIG. 6 is a diagram illustrating the structure of a plasmagenerator of a plasma ignition device for directly igniting a pulverizedcoal boiler according to the present invention;

[0023]FIG. 7 is a diagram illustrating the operating principle of theplasma generator shown in FIG 6.

DETAILED DESCRIPTION OF THE INVENTION

[0024] Now the preferred embodiment of the present invention will bedescribed in details with reference to the accompanying drawings.

[0025] First all the reference signs in the figures will be described inthe following table. 101 pulverized coal burner 102 plasma generator 103bracket 201 burner nozzle 202 fourth stage burning chamber 203 burnerexternal cylinder 204 third stage burning chamber 205 auxiliary airinner cylinder 206 second stage burning chamber 207 powder-air tubes 208external cylinder of the first stage burning chamber 209 auxiliary airinlet tube 210 primary air guide plate 211 the flange of the first stageburning chamber 212 first stage burning chamber 213 high-temperatureplasma transporting pipe 214 guide plate of the first stage burningchamber 215 inlet tube of the first stage burning chamber 216 inlet tubeof the second stage burning chamber 217 primary air-powder tube 218adjustable guide plate for adjusting the powder concentration 219 guideplate for the second stage burning chamber 220 powder channel for thethird stage burning chamber 221 link board 222 auxiliary air channel 223auxiliary air channel 301 cathode head 302 cathode plate 303 coolingnozzle 304 cathode external cylinder 305 water inlet pipe 306 cathodeend cap 307 water outlet tube 308 water supply tube 310 sealing washer311 arc-starting bush 312 conductor sheet 401 sealing ring 402 cathodehousing 403 cooling water 404 anode nozzle tube 405 anode body 406 anodebase 407 water supply tube 408 water outlet tube 501 pulverized coalburner 502 auxiliary air tube 503 electromagnetic coil 504 anode 505compressed air inlet tube 506 cathode 507 dc power supply 508 primaryair inlet tube 601 linear induction motor 602 combined type cathode 603electromagnetic coil 604 composite anode 605 arc transporting coil 606anode water inlet tube 607 anode water outlet tube 608 cathode air inlettube 609 cathode water outlet tube 610 cathode water inlet tube 12arc-starting coil 14 compressed air outlet 15 insulating cylinder

[0026] As shown in FIG. 3, a combined type cathode used in a plasmaignition device, comprises cathode head 301, tight nuts, electricallyconductive tube 304, water inlet tube 308, water inlet pipe 305, wateroutlet tube 307, cathode end cap 306 and sealing cushion 310, saidcathode head 301 is welded to the tight nuts of copper, saidelectrically conductive tube 304 is jointed to the nuts by screwedconnection, a water inlet tube 308 is inserted into the other end of theelectrically conductive tube 304, and is jointed thereto by welding orscrewed connection, a water outlet tube 307 is mounted by welding in thedirection perpendicular to the electrically conductive tube 304, therebya cooling system of the cathode is formed, characterized in that on thefront end of the cathode is mounted a dedicated arc-starting bush 311,the cathode plate 302 is made of alloy plate, and a cooling nozzle 303for cooling the cathode plate is jointed to the water inlet tube 308through welding and is arranged in the center of the electricallyconductive tube 304, said cooling nozzle is constructed so that it isfirst convergent and then divergent.

[0027] According to a preferred embodiment, the arc-starting bush 311 ismade of graphite rod, which has high fusion temperature and highelectrical conductivity, the arc-starting bush 311 is fastened on thefront end of the cathode head 301 through screwed connection, and isflush with the cathode plate 302.

[0028] According to another preferred embodiment, the cathode plate 302is made of Ag-based alloy plate, which has high thermal conductivity andhigh electrical conductivity, the cathode plate 302 is jointed to thecathode head 301 through brazing, and is flush with the arc-startingbush 311. Adopting plate-type cathode enables the self-contracting ofthe arc starting point.

[0029] During the operation of the plasma ignition device adopting abovecombined type cathode, as shown in FIG. 7, when the combined typecathode 602 has been in contact with the anode 603, the dc power supply507 is powered on and the current load is set. When the combined typecathode 602 departs slowly from the anode 603, an electric arc is firstformed between the anode 603 and the arc-starting bush 311. Due to theeffects of mechanical compression, magnetic compression and thermalcompression, the electric arc is quickly transferred from thearc-starting bush 311 to the central cathode plate 302. The revolvingair-flow coming from the compressed air outlet 14 become plasma underthe action of the energy of the electric arc. Experiments show that theburning loss of the anode during arc starting is much fewer and the lifeof the node is extended.

[0030] In addition, since the cooling nozzle of the cooling system ofthe cathode adopts a nozzle tube has a structure that is firstconvergent and then divergent, the liquid is accelerated in the throatportion of the nozzle, so that the efficiency of the heat exchange ofthe cathode is improved and the life of the cathode is lengthened.

[0031] As shown in FIG. 1, the plasma ignition device for directlyigniting a pulverized coal boiler of the invention comprises a plasmagenerator 102, a pulverized coal burner 101, and a plasma generatorbracket 103.

[0032] Through flange connection, the plasma generator 102 has itscomposite anode 604 inserted into the first stage burning chamber 212 ofthe pulverized coal burner. As shown in FIG. 6, said plasma generatorcomprises composite anode 604, combined type cathode 602, linear motor601, electromagnetic coil 603 and arc transporting coil 605 mountedsurrounding the housing of the composite anode 604. The composite anode604 and the combined type cathode 602 are arranged in the same axis. Thecomposite anode is connected to the positive pole of the dc power supply508, and the combined type cathode 602 is connected to the negative poleof the dc power supply 508. The linear motor serves for making saidcathode and said anode to contact each other and then pulling them apartfrom each other so that a plasma electric arc could be established.

[0033] As shown in FIG. 4, the composite anode is constructed as doublenozzle tubes, that is, the composite anode is formed by welding a pairof nozzle tubes. One end of the composite anode is welded to the anodenozzle 404, and the other end is welded to the anode base 406. Saidanode body 405 is made of material of high thermal conductivity and highelectrical conductivity and the oxide of which is also electricallyconductive, such as Ag-based material. The anode nozzle 404 may be madeof cu-based or Ag-based material.

[0034] As shown in FIG. 3, said combined type cathode comprises cathodehead 301, arc-starting bush 311, tight nuts, cathode plate 302, coolingnozzle 303, electrically conductive tube 304, water inlet tube 308,water inlet pipe 305, water outlet tube 307 and cathode end cap 306. Thecathode plate 302 is in form of an inversed cone, and is made ofAg-based alloy. The cooling nozzle 303 is constructed so that it isconvergent first and then divergent.

[0035] As shown in FIG. 2, said pulverized coal burner 101 comprisesburner nozzle 201, fourth stage burning chamber 202, third stageburning. chamber 204, inlet tube 216 of the second stage burningchamber, primary air-powder tube 217, auxiliary air inlet tube 209,guide plate 214 of the first stage burning chamber, guide plate 219 forthe second stage burning chamber and powder channel 220 for the thirdstage burning chamber. The mixture of the air and the pulverized coalflow coming through the primary air-powder tube 217 is divided by thepowder-concentration-adjusting guide plate 218 into three streams, whichrespectively enter into said three stages of burning chambers and burntherein. The auxiliary air coming through the auxiliary air inlet tube209 is divided into three streams, which respectively cool andsupplement oxygen to the outer wall of the first stage burning chamber212, the outer wall of the third stage burning chamber 204 and the innerand outer walls of the fourth stage burning chamber 202.

[0036] The principle and the operation of the invention will bedescribed below with reference to FIG. 5. When the dc power supply 508is powered on, the linear motor 507 is started and advances, so that thecathode 506 contacts the anode 504. At the same time, the output currentand the air pressure of the compressed air inlet tube 505 are set. Withthe cathode departing slowly from the anode, an electric arc voltage isestablished. Since arc voltage is a function of the distance between thetwo electrodes, the distance shall be determined depending on the typeof the coal, so that the power of the art and the voltage may bedetermined. The ionized air carrying energy form a plasma flambeau andenters into the first stage burning chamber 212 of the pulverized coalburner, thereby ignite the high concentration pulverized coal passingthrough the inlet tube 215 of the first stage burning chamber.

[0037] At the same time, the pulverized coal introduced by the primaryair-powder tube 217 is divided by the coal-concentration-adjusting guideplate into three streams, which enters into the burner body. A firstportion of 20% of the high concentration pulverized coal enters into thefirst stage burning chamber through the inlet tube 215 of the firststage burning chamber and the guide plate of the first stage burningchamber, and is ignited by said plasma flambeau. The second stream, 60%of the high concentration pulverized coal enters into the second stageburning chamber through the inlet tube 216 of the second stage burningchamber and the guide plate of the second stage burning chamber. Thethird stream, 20% of the high concentration pulverized coal enters intothe third stage burning chamber through the primary air-powder guideplate and the powder channel for the third stage burning chamber.

[0038] Wherein, the auxiliary air passes through the auxiliary air inlettube of the powder-air tube and enters into the burner by two ways. Theair of one way passes through the upper inlet of the external cylinderof the first stage burning chamber to cool the outer wall of the firststage burning chamber, and then supplements oxygen for burning. The airof the other way passes through the auxiliary air channel to cool theouter wall of the third stage burning chamber, and then is furtherdivided into two streams, one of which enters into the fourth stageburning chamber to supplement oxygen for burning, the other of whichpasses through the auxiliary air channel to cool the fourth stageburning chamber, then enters into the burner hearth.

[0039] Thus, when the high-temperature plasma transporting tube providesa high-temperature plasma, as described above, the first portion of 20%of the high concentration pulverized coal is ignited immediately, theflame thereof further ignites the second portion of 60% of thepulverized coal, the rest 20% of the pulverized coal passes though thepulverized coal channel of the third stage burning chamber and mixeswith above said flambeau and burns. The last portion of the powder-airflow also serves to cool the second stage burning chamber.

[0040] Experiments show that when the amount of pulverized coal in theburning chambers is 500 kg/h, the shape of the flame is Φ700×3000 mm.The flame ignites the pulverized coal in the second stage burningchamber 206 and the third stage burning chamber 204. When the totalamount of the pulverized coal is 5000 kg/h, the temperature of the flameis greater than 1200°C., the jetting velocity at the nozzle is about45-55 m/s, and the shape of the flame is approximately Φ1000×7000 mm.When adopting four plasma ignition devices in straight-flow burner,tangential firing may be maintained, thus starting ignition and stablecombustion may be realized.

1. A plasma ignition device for directly igniting a pulverized coalburner, comprises plasma generator (102), pulverized coal burner (101),plasma generator bracket (103) and dc power supply (508), characterizedin that said plasma generator comprises combined type cathode (602),composite anode (604), electromagnetic coil (603), arc transporting coil(605) and linear motor (601), and said pulverized coal burner (101)comprises powder-air tubes (207), inlet tube (215) of the first stageburning chamber, inlet tube (216) of the second stage burning chamber,primary air-powder tube (217), first stage burning chamber (212), secondstage burning chamber (206), third stage burning chamber (204), fourthstage burning chamber (202), burner nozzle (201) andpowder-concentration-adjusting guide plate (218).
 2. The plasma ignitiondevice for directly igniting a pulverized coal burner according to claim1, characterized in that, said combined type cathode (105) of saidplasma generator (102) comprises cathode head (301), arc-starting bush(311), tight nuts, cathode plate (302), cooling nozzle (303),electrically conductive tube (304), water supply inlet tube (308), waterinlet pipe (305), water outlet tube (307) and cathode end cap (306). 3.The plasma ignition device for directly igniting a pulverized coalburner according to claim 1 or 2, characterized in that, said cathodeplate (302) is in shape of a cylinder plus a cone, and is attached tothe cathode head (301) through welding, and is made of Ag-basedmaterial, which is highly electrically conductive and highly thermallyconductive, and the oxide of which is also conductive; the coolingnozzle (303) is constructed so that it is convergent first and thendivergent.
 4. The plasma ignition device for directly igniting apulverized coal burner according to claim 1, characterized in that, saidcomposite anode (604) of said plasma generator (102) comprises sealingring (401), cathode housing (402), cooling water (403), anode nozzle(404), anode body (405), anode base (406), water supply tube (407) andwater outlet tube (408), said composite anode (604) is formed by weldinga two nozzle tube structures, one end of said composite anode is weldedto the anode nozzle (404), and the other end is welded to the anodebase.
 5. The plasma ignition device for directly igniting a pulverizedcoal burner according to claim 1 or 4, characterized in that, said anodebody (405) is made of Ag-based alloy, and the anode nozzle (404) is madeof copper or Ag-based alloy.
 6. The plasma ignition device for directlyigniting a pulverized coal burner according to claim 1, 4 or 5,characterized in that, said composite anode (604) is surrounded by anarc transporting coil (605).
 7. The plasma ignition device for directlyigniting a pulverized coal burner according to claim 1, characterized inthat, said pulverized coal burner (101) comprises burner nozzle (201),first stage burning chamber (212), second stage burning chamber (206),third stage burning chamber (204), fourth stage burning chamber (202),powder-air tubes (207), primary air-powder tube (217), auxiliary airinlet tube (209), primary powder-air guide plate (210),powder-concentration-adjusting guide plate (218), these components areassembled together through welded link board or through bolting,wherein, the pulverized coal flow coming through the primary air-powdertube (217) is divided into three streams, which respectively passthrough guide plate (214) of the first stage burning chamber, guideplate (219) for the second stage burning chamber and primary powder-airguide plate (210), respectively into specified first stage burningchamber (212), second stage burning chamber (206) and third stageburning chamber (204); the auxiliary air coming from the auxiliary airinlet tube (209) is divided into three streams, which respectively coolsthe external cylinder (208) of the first stage burning chamber, thirdstage burning chamber (204) and the external wall of the fourth stageburning chamber (202), a portion of the auxiliary air enters into theinner wall of the fourth stage burning chamber (202) and the outer wallof the first stage burning chamber (212) so as to supplement oxygen forfacilitating the combustion, the high concentration pulverized coal inthe first stage burning chamber (212) is changed by the guide plate(214) of the first stage burning chamber from radial flow into axialflow, and the powder-concentration-adjusting guide plate (218) adjuststhe concentration of the pulverized coal to a concentration facilitatingthe ignition.
 8. A combined type cathode used in a plasma ignitiondevice, comprises cathode head (301), tight nut(s), electricallyconductive tube (304), water inlet tube (308), water inlet pipe (305),water outlet tube (307), cathode end cap (306) and sealing cushion(310), said cathode head (301) is welded to the tight nut(s) of copper,said electrically conductive tube (304) is jointed to the nut(s) byscrewed connection, a water inlet tube (308) is inserted into the otherend of the electrically conductive tube (304), and is jointed thereto bywelding or screwed connection, a water outlet tube (307) is mounted bywelding in the direction perpendicular to the electrically conductivetube (304), thereby a cooling system of the cathode is formed,characterized in that on the front end of the cathode is mounted adedicated arc-starting bush (311), the cathode plate (302) is made ofalloy plate, and a cooling nozzle 303 for cooling the cathode plate isjointed to the water inlet tube (308) through welding and is arranged inthe center of the electrically conductive tube (304), said coolingnozzle is constructed so that it is first convergent and then divergent.9. The combined type cathode according to claim 8, characterized in thatthe arc-starting bush (311) is made of graphite rod, which has highfusion temperature and high electrical conductivity, the arc-startingbush (311) is fastened on the front end of the cathode head (301)through screwed connection, and is flush with the cathode plate (302).10. The combined type cathode according to claim 8 or 9, characterizedin that the cathode plate (302) is made of Ag-based alloy plate, whichhas high thermal conductivity and high electrical conductivity, thecathode plate (302) is jointed to the cathode head (301) throughbrazing, and the surface thereof is flush with the arc-starting bush(311).